The present invention relates to a circuit arrangement for weighting a current as a function of its magnitude and direction in a receiver circuit for telegraph and data systems engineering.
In telegraph engineering, single current or double current signals are employed for transmitting the information and a sequence of control criteria. In the first instance, current pulses on the line alternate with a no-current condition on the line. In the second instance, pulses of one polarity are interleaved with pulses of the opposite polarity. Devices for telegraph engineering including the modes of transmission used therein are increasingly being utilized for data transmission. Thus the problems of weighting said signals at the receiving end also increase in importance.
In a receiver circuit for telegraph and data systems engineering two problems are presented. It is necessary to differentiate, in the case of single current, between a current pulse and the no-current condition of the line. In the case of double current, a current pulse with a positive polarity must be differentiated from one with a negative polarity. It must also be detected if, in the case of single current system, there is a change of current polarity; and, in the case of double current system, the "no-current" condition must be detected if it prevails. Thus, in both cases, in addition to the conditions established by information signals sought to be transmitted, the conditions outlined herein must be detected.
It is known to carry out weighting of a current of a specified magnitude using threshold responsive weighting means. To weight currents having different polarities, it is known to provide two weighting means set to a specified threshold which deliver an output signal, to an interpreting circuit when the threshold is exceeded. To provide the function of weighting the current independently of direction or polarity, the weighting means are looped into the receiver line over appropriately polarized rectifiers. However, such a current-weighting device requires that both weighting means have a very accurate threshold response. This requisite condition is significant, because with each change of the threshold in a weighting means, the incoming signal on the receiving line is distorted upon being scanned. Further, despite the substantial amount of circuitry utilized, external influences or component tolerances have varying effects on both weighting means. Thus the threshold values vary not only with respect to their absolute values but also with respect to each other.